dilator muscle

Iris dilator muscle

The iris dilator muscle (pupil dilator muscle, pupillary dilator, radial muscle of iris, radiating fibers), is a smooth muscle of the eye, running radially in the iris and therefore fit as a dilator. It is innervated by the sympathetic system, which acts by releasing noradrenaline, which acts on α1-receptors.. Thus, when presented with a threatening stimuli that activates the fight-or-flight response, this innervation dilates the iris, thus temporarily letting more light reach the retina.